Tetraazaindene-stabilized silver halide photographic emulsions

ABSTRACT

TETRAAZAINDENE COMPOUNDS HAVING THE GENERAL FORMULA   2-R,5-R&#39;&#39;,6-I,7-(HO-)-S-TRIAZOLO(1,5-A)PYRIMIDINE   IN WHICH R REPRESENTS A HYDROGEN ATOM, AN ALKYL OR AN ALKYLTHIO GROUP, AND R&#39;&#39; REPRESENTS AN ALKYL GROUP; AND SALTS THEROF; AS WELL AS THE PROCESS FOR THEIR PREPARATION. THIS INVENTION ALSO RELATES TO THE USE OF SUCH TETRAAZAINDENE COMPOUNDS AS STABILIZERS IN SILVER HALIDE PHOTOGRAPHIC EMULSIONS.

United States Patent 3,573,056 TETRAAZAINDENE-STABILIZED SILVER HALIDE PHOTOGRAPHIC EMULSIONS Terence W. Baldock and Alan N. Ferguson, Harlow, Essex, England, assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn.

No Drawing. Filed Dec. 5, 1967, Ser. No. 688,018 Claims priority, application Great Britain, Dec. 8, 1966, 55,114/66 Int. Cl. G03c 1/34 US. Cl. 96109 7 Claims ABSTRACT OF THE DISCLOSURE Tetraazaindene compounds having the general formula in which R represents a hydrogen atom, an alkyl or an alkylthio group, and R represents an alkyl group; and salts thereof; as well as the process for their preparation. This invention also relates to the use of such tetraazaindene compounds as stabilizers in silver halide photographic emulsions.

This invention relates to heterocyclic compounds and in particular tetraazaindene compounds and to the use of these compounds in the stabilization of silver halide photographic emulsions.

The tetraazaindene compounds in accordance with the invention are the 4-hydroxy-5-iodo-1:3:3a:7tetraazaindenes and they have the general formula:

in which R represents a hydrogen atom, an alkyl or an alkylthio group, and R represents an alkyl group; or a salt thereof.

These compounds are efficient stabilizers when introduced into silver halide photographic emulsions and substantially prevent the formation of chemical fog.

The tetraazaindene compounds of the invention can be prepared by reaction of a diazotized 5-amino-4-hydroxy- 1:3:3a27-tetraazaindene with an alkali metal iodide, such as potassium or sodium iodide, so as to introduce an iodine atom in the 5-position. When diazotization leads to the formation of a diazo oxide, this can be isolated and reacted with an anhydrous solution of hydrogen iodide in dioxane to obtain the S-iodo compound. The diazotized S-amino-tetraazaindene can itself be prepared from a 4- hydroxy-lz3z3az7-tetraazaindene by nitration to substitute an NO group in the 5-position, reduction of the NO group to an amino group (-NH and then diazotization of the amino group.

The tetraazaindene compounds according to the invention may be used as such or in the form of their salt with, for example, ammonium, sodium or potassium hydroxide or carbonate.

The tetraazaindene compounds of the invention are very effective as stabilizers for photographic silver halide emulsions. As is well known, light sensitive silver halide emulsions tend to yield, on development, a deposit of silver in those areas which have not been exposed to light.

3,573,056 Patented Mar. 30, 1971 This deposit, which is commonly termed chemical fog impairs the quality of the image and, indeed, in certain cases may obliterate the image. The tendency to form this fog is more pronounced when the emulsion is of a highly sensitive type and also when the emulsions are stored under adverse conditions, as for example, under the conditions of high temperature and high humidity which are met with in tropical countries. In order to counteract the tendency of silver halide emulsions to form this fog it is common practice to add to them so-called stabilizers. Most of the compounds used as stabilizers are successful to a high degree in preventing the formation of fog, but many of them suffer from the disadvantage that they reduce the sensitivity of the emulsion and also slow down the rate of development of the photographic image.

The tetraazaindene compounds of the invention, on the other hand, although effective in preventing the formation of fog, do not cause any decrease in the sensitivity of the emulsions, and indeed, in some cases they may even increase the sensitivity. Furthermore they have no adverse effect upon the rate of development. It is found that particularly good results are obtained when the substituents R and R in the formula of the reactants given above contain not more than 4 carbon atoms.

Best results have been obtained with emulsions containing from 0.125 millimole to 3.0 millimoles of stabilizer per mole of silver present in the emulsion. The tetraazaindene stabilizing compounds will normally be added at the completion of chemical ripening or digestion of the emulsion, although it may sometimes be possible for the addition to take place at an earlier stage in the preparation of the emulsion. At whatever stage it is added, the solids may be introduced by themselves or as solution in inert solvents such as Water or ethanol.

The tetraazaindene compounds need not necessarily be directly added to the silver halide emulsions in order to give protection to the emulsions against the formation of fog. The compounds have been found effectively to stabilize a layer of silver halide emulsion if that layer is in contact with a layer containing one of the compounds of this invention so that at some time during the manufacture of the photographic film the stabilizer compound can diffuse into the adjacent emulsion layer. This method of effecting stabilization may be particularly advantageous for photographic films which contain a number of layers of silver halide emulsion.

The invention will now be illustrated with reference to the following examples of preparations of compounds in accordance with the invention and their use in stabilizing silver halide photographic emulsions.

EXAMPLE 1 Preparation of 4-hydroxy-5-iodo-6-methyll :3 3a: 7-tetraazaindene 165 g. of S-amino-4-hydroxy-6-methyl-1:3:3a:7-tetraazaindene suspended in 1 liter of water containing 225 g. of concentrated hydrochloric acid, was diazotized with 70 g. of sodium nitrite in ml. Water. The temperature was maintained below 5 C. with external ice cooling. The resulting diazonium salt solution was slowly added to a solution of 400 g. sodium iodide in 1 liter of water containing l g. of copper powder. The temperature during the addition was maintained at 10 C. by external cooling. After complete addition the dark-violet solution was al lowed to stand at room temperature for one hour, then warmed on a steam bath for one hour, cooled and filtered. The solid product obtained was stirred in 2.5 liters of water containing 250 g. of sodium thiosulfate until the color lightened to a light brown. The solid was then filtered off and recrystallized from boiling 2 N acetic acid containing a little charcoal. The desired product Was obtained as almost colourless needles. The yield was 40.9 g., and melting point was 2534 C. with decomposition.

Analysis.Calculated for C H N OI (percent): C, 26.1; H, 1.8; N, 20.3; I, 46.0. Found (percent): C, 25.7; H, 2.3; N, 20.3; I, 45.2.

4 Analysis.-Calculate d for C7HI7N4OSI (percent): C, 26.1; H, 2.2; N, 17.4; S, 9.95. Found (percent): C, 26.4;- H, 2.5; N, 18.0; s, 10.1.

EXAMPLE 4 5 A silver iodobromide h p otograph1c emulslon was EXAMPLE 2 ripened to about 1.2 micron average grain diameter, then Preparation of 2,6-dimethyl-4-hydroxy- Washed and digested in the presence of sodium thiosul- 5-iodo-1:3:3a17-tetraazaindene fate and gold until it reached its maximum speed. This divided into portions which were separately treated 90 g. of 5-2um1no-2,6-d1methyl-4-hydroxy-1:3:3a:7-tetr raazaindene suspended in 500 ml. of water containing 115 zi gg ggi gg s gg gg g gggg 3 35: ml. of concentrated hydrochloric acid, was diazotized with 1 Th 1 p d t 35 g. of sodium nitrite in 75 ml. of water. The tempera- S1 Ver present m t 6 mm Slon' T resu tmg a mlx ure ture was maintained below 5 C with external ice coolwas coated Onto a film base and dne'd' further i 1e g The resulting diazonium a solution was slowly of the emulsion was coated without add1t1on of stabilizer.

One sample of each coating was kept for four days iii: g i i g g ig ggg g x gf fi ggg g: under nonmal conditions of temperature and humidity ture during addition was maintained at 10 C by exter- Whlle anoflger samp 1c of each was g g ifi sang: penfd 1n an 1ncu ator at a temperature 0 an a re aof warmed on a steam bath for one hour cooled a trons which approxlmate to a comparatively long shelf terevd The 801i d product Obtained Was stirred in 1 1i ter of l fe under normal conditions and a somewhat shorter shelf water containing 125 g of sodium thiosulfate for ten minhfe unger trizp if all g i g film a g i fi p expose to lg t an eve ope 1n a 'stan ar meto yutes then filtered off and recrystallized from boiling a ueous alcohol. The desired product was obtained as alri iost droqumone developer The Speed fog and C-Ontrast values colorless needles were then measured. The results are glven 1n Table I.

The d was6 0 d (7 t 227 80 C From these values it will be observedthat the unsta- With mpositiol'l an me p m was bilized emulsion when subjected to a period of high temperature and humidity lost speed and gave increased fog, f gg ig g g g i F 6 25 5 3 while the speed and fog of the emulsion samples contain- Dun Percen 1 ing the stabilizer compound of Example 1 were substan- EXAMPLE 3 tially unaffected by such accelerated storage conditions.

Preparation of 4 hydroxy 5 iodo 6 methyl- EXAMPLE 5 Z-methylmercapto-l:3z3az7-tetraazaindene A silver iodobromide photographic emulsion was 53 of 5 amino 4 hydroxy 6 methyl z methylmercap ripened to about 1.2 micron average grain diameter, then to-1:3z3az7-teetraazaindene suspended in 300 ml. of water Washad and heated m t Presence of Sodium thiosulfate containing 57 g. of concentrated hydrochloric acid, was and gold h optlmilm f of contrast diazotized with 18 g. of sodium nitrite in 50 ml. of water. Speed .l q .Thls 61211510 was cooled rapldly The temperature was maintained below C. with exter 40 and divided into portions which were separately treated nal ioe cooling. A suspension of the diazo oxide was obwith. Stabilizers of Examples 1 to 3 and the Standard tained which was stirred for one hour and then filtered l i 4 t 01f, washed free of acid with water and dried. The yield Whlch. 1s stziblhzer compionly used m present photo" was 55 g graph1c films 1n the quantities shown in Table II.

A portion of this compound was recrystallized from The.resultmg admlxture was coated on.to a film base boiling ethanol to give yellow crystals of melting point P dned' .further i i of the emulslon was coated with decomposition without add1t1on of stablhzer.

Analysis.Calculated for C H N OS (percent): 0, one Sample coatmg was kept for 62 1? 379; H 2]; N 379; S 144' Found (percent), C 38 under normal conditlons of temperature and humidity H, 2.4; N, 37.9; S, 150; while another sample of each was kept for the same 150 ml. of dry dioxane was stirred at room temperapenod.m an lpcpbator at a Eemperature of 70 ture while dried hydrogen iodide was bubbled through it. reliiglve hmmdlty of under t agmg When 20 g. of hydrogen iodide had been absorbed the condltions Whlch approxlmfiie to a comparatively long dioxane was poured Onto 10 g of the diazo Oxide shelf lrfe under normal condltions and a somewhat shorter pared as described above. There was an immediate reac- Shelf hfe under conditions) The i was Subtion, nitrogen was given 011 and the reaction mixture sequenfly expo-56d to hght and developed m a standard warmed spontaneously to about 40 C. After stirring for figftg xi z ys gj 121325255 2 39;? fi i? (gong 30 minutes the solution was evaporated to dryness at reare given in fa IL resu S 0 mm duced pressure h resldPe Was grow? up with acefonea 60 From these values it will be observed that the unz gg l thetsohd obtimed Washed Wlth ijlcetonfe all stabilized emulsion, when subjected to a period of inl 0 an gave 1ncrease 0g, w e t e spee an 0g of the acetic ac d to g ve off-white needles. The yleld was 2.3 g. emulsion samples containing the stabilizer compounds and melting polnt 2505 C. with dECOmPOSItIOII. were substantially unaifected by such storage conditions.

TABLE I 4 days under ordinary 4 days incubation at 125 conditions F. and R.H.

Quantity Relative Relative millimoles/ speed 0.5 speed 0.5 Compound mole Ag Fog 7 above tog Fog 7 above fog None 0. 70 0.87 Compound prepared in Example 1 1. 0: 20 2: 70 1: 20 0:24 3.0 0. 24 2. 75 1.17 0.32 2.15 1.22

TABLE II 62 hrs. incubation at 70 C. and 62 hrs. under ordinary conditions 30% R.H.

Quantity Relative Relative milhmoles/ Maximum speed 0.5 Maximum speed Compound mole Ag Fog contrast (1 above fog Fog contrast above fog None 0. 1 1. 44 1. 5s 0. 27 1. 37 1. 53 Standard 3.0 0.08 1. 33 1. 64 0.15 1. 46 1. 63 Compound prepared in Example 1 0. 5 0. 11 1. 35 1. 52 0. 11 1. 51 1. 57 Compound prepared in Example 2 0.25 0. l. 35 1. 57 0.12 1. 28 1. 57 Compound prepared in Example 3 0. 125 0. 08 1.27 1 52 0.08 1. 30 1. 59

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A silver halide photographic emulsion which contains a stabilizing amount of a tetraazaindene compound having the general formula in which R represents a hydrogen atom, an alkyl group or an alkylthio group, and R represents an alkyl group; or a salt thereof.

2. An emulsion as claimed in claim 1 which contains no more than 3.0 rnillimoles of the tetraazaindene compound per mole of silver present in the emulsion.

3. An emulsion as claimed in claim 2 which contains from 0.125 to 3.0 millimoles of the tetraazaindene compound per mole of silver present in the emulsion.

4. The emulsion of claim 1 wherein said tetraazaindene compound is 4 hydroxy-S-iodo-G-methyl-1:3:3a:7-tetraazaindene.

5. The emulsion of claim 1 wherein said tetraazaindene compound is 2,6 dimethyl4-hydroxy-5-iodo-1:3:3a:7- tetraazaindene.

6. The emulsion of claim 1 wherein said tetraazaindene compound is 2 methylmercapto 4hydroXy-5-iodo-6- methyl-1 :3 3a: 7-tetraazaindene.

7. Photographic film containing at least one silver halide photographic emulsion layer stabilized with a tetraazaindene compound of the formula or an alkylthio group, and R represents an alkyl group; or a salt thereof.

References Cited UNITED STATES PATENTS 2,716,062 8/1955 Carroll et al. 96107X 2,784,091 3/1957 Carroll et al. 96-107X 2,835,581 5/1958 Tinker et al. 96107X WILLIAM D. MARTIN, Primary Examiner T. G. DAVIS, Assistant Examiner 

